Embodiments of the invention relate to a pixel unit of a fringe field switch (FFS) type thin film transistor liquid crystal display (TFT-LCD) array substrate.
TFT-LCDs have been an important type of flat panel displays (FPDs). TFT-LCDs can be classified into a vertical electrical field type and a horizontal electrical field type depending on the direction of the electrical field by which liquid crystal is driven. For a vertical electrical field type TFT-LCD, a pixel electrode is formed on an array substrate while a common electrode is formed on a color filter substrate. For a horizontal electrical field type TFT-LCD, both a pixel electrode and a common electrode are formed on an array substrate. Therefore, an additional patterning process for forming the common electrode is required when a horizontal electrical filed type TFT-LCD array substrate is manufactured. A vertical electrical field type TFT-LCD comprises a twist nematic (TN) type TFT-LCD. A horizontal electrical field type TFT-LCD comprises a fringe field switching (FFS) type TFT-LCD and an in-plane switching (IPS) type TFT-LCD. A horizontal electrical field type TFT-LCD, especially an FFS type TFT-LCD, has advantages such as wide view angles and high aperture ratio and have been widely used in the liquid crystal display filed.
There are various kinds of FFS type TFT-LCDs; however, these different kinds of FFS type TFT-LCD have a common point: a horizontal electrical field is generated through a plate electrode and a slit electrode. The positions of the plate electrode and the slit electrode may be different. The plate electrode may be a common electrode or a pixel electrode, and the slit electrode may also be a common electrode or a pixel electrode accordingly.
FIGS. 1 and 2 are schematic plan views of a conventional slit electrode. FIG. 1 shows an alignment of liquid crystal when no voltage is applied. FIG. 2 shows an alignment of liquid crystal after a driving voltage is applied. As shown in FIGS. 1 and 2, for the conventional slit electrode, the sum of the width W of an electrode parts 12′ between two slits 11′ and the width L of the slits 11′ adjacent to the electrode part 12′ has a constant value. The rotation of liquid crystal molecules is affected by the driving voltage and the value of W+L. Since the value of W+L for the conventional slit electrode is a constant value across the electrode, the liquid crystal molecules driven by the applied driving voltage will have the same rotation degree across a pixel unit.
The optical characteristics of liquid crystal molecule render the light refractive index different when viewed from various view angles. When the view angle is switched from the front to one side of a liquid crystal display panel, i.e., the incident angle of the light is changed, the light refractive index difference of liquid crystal becomes more and more notable. Since each liquid crystal molecule has the same rotation degree, the light refractive index at a certain view angle is the same. Therefore, since the average light refractive index of liquid crystal varies to a relatively large degree for the whole panel, the image quality becomes different when the image is viewed from the front and from the side.
In the conventional liquid crystal display, the image quality various notably when viewed from different view angles, which leads to the users' dissatisfaction with the product performance.